The present invention relates to apparatus by which gating means for directing signals from a photoelectric detector to separate storage channels is synchronized with the positions of a beam switch which sequentially directs light from different beams to the photoelectric detector. Beam switches are commonly used in analytical equipment, such as atomic absorption spectrophotometers where the readout is mathematically related to the output signal of the photoelectric detector at each position of the beam switch. Therefore, circuit means must be provided for processing the detector output signals to the desired mathematical result. Of course, noise is always a problem where signals are processed directly from the photoelectric detector, due to the step nature of such signals. Although gating circuits may have been known for controlling storage channels which would have resolved this problem, to synchronize such circuits with the sequential positions of the beam switch was unknown in the art.